Production of phosphoric acid of high purity

ABSTRACT

A process for production of phosphoric acid of high purity from crude phosphoric acid obtained by decomposition of an ore of phosphorus with sulfuric acid which comprises extracting the crude phosphoric acid with a water-immiscible organic solvent selected from the group consisting of alkanols having 6 to 8 carbon atoms and ethers of polyvalent alcohols with alkanols having 3 to 8 carbon atoms, washing the resulting extract at least 4 times with water, optionally containing phosphoric acid, the total amount of the water for washing being 25 to 50 parts by weight to 100 parts by weight of the phosphoric acid contained in the extract, and back extracting the washed extract with water, optionally followed by concentration of the resultant water extract.

United States Patent [191 Takahara [4 1 Nov. 4, 1975 PRODUCTION OF PHOSPHORIC ACID OF HIGH PURITY [22] Filed: Apr. 5, 1974 [21] Appl. No.: 458,369

[30] Foreign Application Priority Data Oct. 12, 1973 Japan 48-115084 [52] US. Cl. 423/321; 423/320 [51] Int. Cl. C01B 25/16 [58] Field of Search 423/320, 321, 321 S [56] References Cited UNITED STATES PATENTS 3,410,656 11/1968 Bunin et a1. 423/321 S FOREIGN PATENTS OR APPLICATIONS 180,569 11/1966 U.S,S.R 423/321 1,209,272 /1970 United Kingdom 423/321 S Primary Examiner0scar R. Vertiz Assistant ExaminerEugene T. Wheelock [57] ABSTRACT A process for production of phosphoric acid of high purity from crude phosphoric acid obtained by decomposition of an ore of phosphorus with sulfuric acid which comprises extracting the crude phosphoric acid with a water-immiscible organic solvent selected from the group consisting of alkanols having 6 to 8 carbon atoms and ethers of polyvalent alcohols with alkanols having 3 to 8 carbon atoms, washing the resulting extract at least 4 times with water, optionally containing phosphoric acid, the total amount of the water for washing being to parts by weight to parts by Weight of the phosphoric acid contained in the extract, and back extracting the washed extract with water, optionally followed by concentration of the resultant water extract.

5 Claiins, No Drawings The present invention relates to a process for production of phosphoric acid. More particularly, it relates a process for production of phosphoric acid of high purity, i.e. markedly reduced in its content of inorganic impurities.

Crude phosphoric acid obtained by decomposition of an ore of phosphorus with mineral acids such as hydrochloric acid and sulfuric acid usually includes considerable amounts of inorganic impurities such as iron, arsenic, aluminum, lead, vanadium, titanium, silica, sulfate and chloride. For removal of the inorganic impurities from the crude phosphoric acid to obtain a high purity of phosphoric acid, there has been proposed the socalled solvent extraction process wherein various water-immiscible organic solvents are used for extraction of phosphoric acid. There have also been proposed many processes which can eliminate some drawbacks found in the solvent extraction process.

The solvent extraction process generally comprises the treatment of crude phosphoric acid obtained by decomposition of an ore of phosphorus with a waterimmiscible organic solvent to extract the phosphoric acid and the subsequent treatment of the extract with water to back extract the phosphoric acid. In the treatment with the water-immiscible organic solvent in the first step, the inorganic impurities present in the crude phosphoric acid are more or less extracted into the organic solvent. Therefore, the subsequent treatment of the resulting organic extract with water can not prevent the movement of the inorganic impurities into the water and the resultant phosphoric acid solution is somewhat contaminated with the inorganic impurities.

In order to overcome such a drawback, there have been proposed various processes for removal of the contaminating inorganic impurities from the phosphoric acid solution, some examples of which are as follows:

1. Removal of silica: Japanese Patent Publications Nos. 15893/1968 and 30174/1968;

2. Removal of calcium: Japanese Patent Publication No. 17284/1968;

3. Removal of arsenic and iron: Japanese Patent Publications Nos. 8252/1962 and 11/1963;

4. Removal of sulfate: Japanese Patent Publication No. 7753/1964;

5. Removal of chloride: Japanese Patent Publications Nos. 10016/1960, 8252/1962, l1/l963, 13603/1963 and 7753/1964.

However, all these conventional processes are not industrially satisfactory, for instance, since they require troublesome operations, need expensive or large apparatus, or produces phosphoric acid with insufficiently high purity and the like. Among the above, the processes using ion exchange resins for removal of the inorganic impurities (cf. Japanese Patent Publications Nos. 8252/1962, ll/l963, 17284/1968, etc.) are relatively favorable in the satisfactory purity of the resulting phosphoric acid but still have a certain disadvantage, for instance, in the high production cost of phosphoric acid due to the use of comparatively expensive ion exchange resins.

As the result of an extensive study, it has now been found that the inorganic impuritiesunavoidably contaminating the phosphoric acid extract obtained by extraction of crude phosphoric acid with a water-immisci- 2 ble organic solvent, can be efficiently eliminated by washing such an organic extract with water under a certain conditions and the back extraction of the washed organic extract with water can produce a solution of phosphoric acid of satisfactorily high purity. That is, the adoption of a simple operation such as multiple water washings between the extraction with a waterimmiscible organic solvent and the back extraction with water makes it possible to obtain a high purity of phosphoric acid without using such an expensive material as an ion exchange resin. The present invention is based on the above finding.

The process of this invention comprises extracting crude phosphoric acid, which is obtained by decomposition of an ore of phosphorus with sulfuric acid, with a water-immiscible organic solvent selected from the group consisting of alkanols having 6 to 8 carbon atoms and ethers of polyvalent alcohols with alkanols having 3 to 8 carbon atoms, washing the resulting extract at least 4 times with water, optionally containing phosphoric acid, the total amount of the water for these washings being 25 to 50 parts by weight to parts by weight of the phosphoric acid contained in the extract, and back extracting the washed organic extract with water, optionally followed by concentration of the resultant water extract to give phosphoric acid of high purity.

Examples of the alkanols having 6 to 8 carbon atoms are 2-octanol, 2-ethylhexanol, 3-methylhexanol, 5- methylhexanol, etc. Examples of the ethers of polyvalent alcohols with alkanols having 3 to 8 carbon atoms are diethyleneglycol di-n-butyl ether, glycol di-n-butyl ether, etc. These organic solvents will be hereinafter referred to as water-immiscible organic solvent".

The extraction of the crude phosphoric acid with the water-immiscible organic solvent may be carried out batchwise or continuously at a temperature from room temperature to about 100C.

When sulfuric acid isused in excess for completion of the decomposition of an ore of phosphorus, a considerable amount of sulfuric acid may be present in the resulting crude phosphoric acid. In such case, calcium hydroxide or barium hydroxide may be added thereto so, that the sulfuric acid is precipitated in the form of calcium sulfate or barium sulfate. The resultant slurry is subjected to extraction with the water-immiscible organic solvent and then the resulting organic extract is subjected to the treatment for purification as hereinafter described.

The the water-immiscible organic solvent extract is then repeatedly washed with water, optionally containing phosphoric acid. The washing should be repeated at least 4 times, preferably at least 6 times, the total amount of water used being 20 to 50 parts by weight to 100 parts by weight of the phosphoric acid contained in the organic extract. When the content of each inorganic impurity in the washing water is less than 1 ppm, the washing operation is terminated. The washing is usually effected at room temperature.

Then, the washed organic extract is back extracted with water optionally containing phosphoric acid, usually at a temperature from room temperature to about 100C (preferably from about 60 to 100C). No limitation is present on the proportion of the extract and the water, but the amount of the water should be as little as possible.

The resultant water extract, i.e. aqueous solution of phosphoric acid, is usually concentrated. However, this 3 concentration operation is optional.

The water-immiscible organic solvent after the back extraction may be again used for extraction of the crude phosphoric acid. When contaminated to a con- 4 washings are checked each time. When the content of each inorganic impurity is less than 1 ppm, the washing operation is stopped. The organic layer after the washing is back extracted with water (100 g) at room temsiderable extent, it may be purified, for instance, by perature. in the resulting aqueous extract, i.e. aqueous washing with an alkali carbonate solution or treating solution of phosphoric acid, the presence of 75 g of with activated carbon. phosphoric acid is confirmed. The content of each in- Further, the aqueous phase after the extraction of the organic impurity as examined is trace, and the quality crude phosphoric acid with the water-immiscible orof the phosphoric acid solution meets the requirements ganic solvent, as well as the water washings produced in in HS (Japanese Industrial Standard) Kl449-l957. the washing of the water-immiscible organic solvent ex- The aqueous phase separated in the extraction with tract of phosphoric acid may be combined into the 2-octanol and the washings obtained in the washing crude phosphoric acid, and then the resulting mixture treatment are combined into the starting crude phosmay be subjected to extraction with the water-immisciphoric acid and again subjected to extraction with 2- ble organic solvent as above. Thus, the phosphoric acid octanol. Therefore, phosphoric acid can be recovered in the system is not materially lost. without any material loss. The organic layer after the Practical and presently preferred embodiments of the back extraction is used again for the extraction of invention are illustratively shown in the following Excrude phosphoric acid. amples. The amount of phosphoric acid and the contents of EXAMPLE 1 the inorganic impurities at various stages in the process of this Example are analyzed and shown in Table I.

Table 1 Phosphoric acid R 0, AS Al o Aqueous Solvent Aqueous Solvent Aqueous Solvent Aqueous Solvent phase phase phase phase phase phase phase phase Crude phosphoric acid (150 g) 0.89 0.3 0.17 Extraction with solvent g) g) 0.63 0.23 0.21 0.09 0.12 0.05 Washing lst with (20 g) (4.5 g) (85.5 g) 0.14 0.09 0.07 0.02 0.042 0.008 water 2nd (Amount (20 g) (4.6 g) (80.9 g) 0.07 0.02 0.018 0.002 0.007 0.001 of 3rd water (10 g) (2.5 g) (78.4 g) 0.013 0.007 0.0018 0.0002 0.0008 0.0002 used) 4th (10 g) (2.7 g) (75.7 g) 0.006 0.001 0.0001 0.0001 0.0001 0.0001 5th (3 g) (0.5 g) (75.2 g) 0.0009 0.000l Trace Trace Trace Trace Back extraction with water (75 g) (0.2 g) Trace Trace s) Pb SiO, CaO S04 Cl AqueousSolvent AqueousSolvent AqueousSolvent AqueousSolvent AqueousSolvent phase phase phase phase phase phase phase phase phase phase Crude phosphoric acid 0.04 1.65 1.32 0.08 0.001 Extraction with Solvent 0.026 0.004 1.48 0.17 1.16 0.16 0.04 0.04 0.008 0.002 Washing 15! with (20 g) 0.0037 0.0003 0.16 cm 0.15 0.01 0.02 0.02 0.0017 0.0003 water 2nd (Amount (20 g) 0.0002 0.0001 0.007 0.0003 0.007 0.003 0.012 0.008 0.0002 0.0001 of 3rd water (10 g) Trace Trace 0.0002 0.000l 0.0023 0.0002 0.006 0.002 Trace Trace used) 4th (10 g) Trace Trace 0.000! 0.001 0.001 0001 5th (3 g) Trace Trace 0.0009 0.0001 Back extraction with water Trace Trace (100 g) 37.5 Crude hos horic acid solution obtained b p p y EXAMPLE 2 decomposition of an ore of phosphorus with sulfuric acid is concentrated, and excess of sulfuric acid therein As in Example 1, 75 crude phosphoric acid soluis neutralized with calcium hydroxide. After filtration 60 tion (200 g) is extracted with Z-ethylhexanol (500 g).

of the precipitated calcium sulfate, the resultant 75 crude phosphoric acid solution (200 g) is admixed with 2-octanol (500 g), and vigorous stirred at room temperature (about 10 to 20C). The aqueous phase is separated from the organic phase. The organic phase, which contains phosphoric acid, is washed five times with water (20 g, 20 g, 10 g, 10 g, 3 g) at room temperature. The contents of the inorganic impurities in the The organic phase, which contains phosphoric acid, is washed five times with water (20 g, 20 g, 10 g, 10 g, 2 g) at room temperature. The contents of the inorganic impurities in the washings are checked each time. When the content of each inorganic impurity is less than 1 ppm, the washing operation is stopped. The organic layer after the washing is back extracted with water (100 g) at room temperature. In the resulting 5 aqueous extract, i.e. aqueous solution of phosphoric acid, the presence of 75 g of phosphoric acid is confirmed. The content of each inorganic impurity as examined is trace, and the quality of the phosphoric acid solution meets the requirements in HS 141449-1957. 5

The amount of phosphoric acid and the contents of the inorganic impurities at various stages in the process of this Example are analyzed and shown in Table 2.

6 tents of the inorganic impurities in the washings are checked each time. When the content of each inorganic impurity is less than 1 ppm, the washing operation is stopped. The organic layer after the washing is back extracted with water (100 g) at room temperature. In the resulting aqueous extract, i.e. aqueous solution of phosphoric acid, the presence of 75 g of phosphoric acid is confirmed. The content of each inorganic Table 2 Phosphoric acid Fe o As 2 Aqueous Solvent Aqueous Solvent Aqueous Solvent Aqueous Solvent phase phase phase phase phase phase phase phase Crude phosphoric acid (150 g) 0.89 0.3 0.17 Extraction with solvent (53 g) (97 g) 0.69 0.20 0.25 0.07 0.12 0.05 Washing lst with (20 g) 4.5 g) (92.5 g) 0.125 0.075 0.046 0.024 0.046 0.004 water 2nd (Amount (20 g) (4.5 g) (87.5 g) 0.065 0.018 0.018 0.006 0.0025 0.0015 of 3rd water (10 g) (2.6 g) (84.9 g) 0.012 0.004 0.0055 0.0005 0.0012 0.0003 used) 4th (10 g) (2.5 g) (82.4 g) 0.0038 0.0002 0.0004 0.0001 0.0002 0.0001 5th (2 B) (0.4 g) (82 g) 0.0001 0.0001 0.0001 0.0001 Trace Trace Back extraction with water (81.5 g) (0.5 g) (1 g) Pb S CaO SO, C1(%) Aqueous Solvent AqueousSolvent AqueousSolvent Aqueous Solvent AqueousSolvent phase phase phase phase phase phase phase phase phase phase Crude phosphoric acid 0.04 1.65 1.32 0.08 0.001 Extraction with solvent 0.039 0.001 1.51 0.14 1.22 0.10 0.05 0.03 0.0007 0.00003 Washing 1st with g) 0.0007 0.0003 0.13 0.01 0.08 0.02 0.023 0007 Trace Trace water 2nd (Amount (20 g) 0.00027 0.00003 0.008 0.002 0.016 0.004 0.006 0.001 of 3rd 7 water (10 g) Trace Trace 0.0019 0.00001 0.0038 0.0002 0.0008 0.0002 used) 4th (10 g) Trace Trace 0.0001 0.0001 0.0001 0.0001 5th (2 g) Trace Trace Back extraction with water (1 8) im urity as examined is trace and the ualit of the EXAMPLE 3 p q y As in Example 1, crude phosphoric acid solution (200 g) is extracted with heptanol (3- or S-methylhexanol) (500 g). The organic phase, which contains phosphoric acid, is washed five times with water (20 g, 20 g, 10 g, 10 g, 2 g) at room temperature. The conphosphoric acid solution meets the requirements in JIS K1449-1957.

The amount of phosphoric acid and the contents of the inorganic impurities at various stages in the process of this Example are analyzed and shown in Table 2.

Table 3 Phosphoric acid Fe,o, As A1 0; Aqueous Solvent Aqueous Solvent Aqueous Solvent Aqueous Solvent phase phase phase phase phase phase phase phase Crude phosphoric acid (150 g) 0.89 0.3 0.17 Extraction with solvent (45 g) (105 g) 0.76 0.13 0.23 0.02 0.14 0.03 Washing lst with (20 g) (4.5 3) (100.5 g) 0.11 0.02 0.017 0.003 0.024 0.006 water 2nd (Amount (20 g) (4.5 g) (96 g) 0.01 0.008 0.002 0.001 0.0058 0.0002 of 3rd water (10 g) (2.5 g) (93.5 g) 0.007 0.001 0.0008 0.0002 0.0001 0.0001 used) 4th (10 g) (2.6 g) (90.7) 0.0008 0.0002 0.0001 0.0001 Trace Trace 5th (2 g) (0.4 g) (90.3 g) 0.0001 0.0001 Back extraction with water g) 8) g) Pb SiO CaO S0 Table 3-continued Phosphoric acid Fe,0, As A1 Aqueous Solvent Aqueous Solvent Aqueous Solvent Aqueous Solvent phase phase phase phase phase phase phase phase Aqueous Solvent Aqueous Solvent Aqueous Solvent Aqueous Solvent AqueousSolvent phase phase phase phase phase phase phase phase phase phase Crude phosphoric acid 0.04 1.65 1.32 0.08 0.001 Extraction with solvent 0.036 0.004 1.52 0.13 1.20 0.12 0.06 0.02 0.0008 0.0002 Washing 1st with g) 0.0037 0.0003 0.127 0.003 0.11 0.01 0.016 0.004 0.0001 0.0001 water 2nd (Amount (20 g) 0.0002 0.0001 0.0023 0.0007 0.008 0.0002 0.0032 0.0003 Trace Trace of 3rd water (10 g) Trace Trace 0.00065 0.00035 0.0001 0.0001 0.0005 0.0003 used) 4th (10 g) Trace Trace Trace Trace Trace Trace 0.0002 0.000l 5th (2 g) Trace Trace Back extraction with water (100 1;)

What is claimed is:

1. A process for production of phosphoric acid, with reduced inorganic impurities, from crude phosphoric acid obtained by decomposition of an ore of phosphorus with sulfuric acid, which comprises extracting the crude phosphoric acid with a water-immiscible organic solvent selected from the group consisting of alkanols having 6 to 8 carbon atoms, washing the resulting extract at least 4 times with water, or water containing phosphoric acid, the total amount of the water for washing being to 50 parts by weight to 100 parts by weight of the phosphoric acid contained in the extract, and back extracting the washed extract with water, to

obtain aqueous phosphoric acid with reduced inorganic impurities.

2. A process, as in claim 1, wherein the product aqueous phosphoric acid is subsequently concentrated.

3. The process according to claim 1, wherein the water-immiscible organic solvent is a member selected from the group consisting of 3-methylhexanol and 5- methylhexanol.

4. The process according to claim 1, wherein the washing with water is carried out at least 6 times.

5. The process according to claim 1, wherein the washing is carried out until the content of each inorganic impurity in the washing water is made to be less than 1 ppm. 

1. A process for production of phosphoric acid, with reduced inorganic impurities, from crude phosphoric acid obtained by decomposition of an ore of phosphorus with sulfuric acid, which comprises extracting the crude phosphoric acid with a water-immiscible organic solvent selected from the group consisting of alkanols having 6 to 8 carbon atoms, washing the resulting extract at least 4 times with water, or water containing phosphoric acid, the total amount of the water for washing being 25 to 50 parts by weight to 100 parts by weight of the phosphoric acid contained in the extract, and back extracting the washed extract with water, to obtain aqueous phosphoric acid with reduced inorganic impurities.
 2. A process, as in claim 1, wherein the product aqueous phosphoric acid is subsequently concentrated.
 3. The process according to claim 1, wherein the water-immiscible organic solvent is a member selected from the group consisting of 3-methylhexanol and 5-methylhexanol.
 4. The process according to claim 1, wherein the washing with water is carried out at least 6 times.
 5. THE PROCESS ACCORDING TO CLAIM 1, WHEREIN THE WASHING IS CARRIED OUT UNTIL THE CONTENT OF EACH INORGANIC IMPURITY IN THE WASHING WATER IS MADE TO BE LESS THAN 1 PPM. 